Resonator tuner



Sept. 6, 1955 M. R. HUBBARD RESONATOR TUNER Original Filed Sept. 18, 1952 w A? I a}; z u g T 3 a 1; u Li z I 4PM:

IH 1 E INVENTOR. Maw! M/aaA/Po United States Patent 'RESONATORTUNER v Merle R. rflubbar'd, Cedar ZRapids, iIowa,-;assignor .to :-Collins Radio Company, Cedar Rapids, ;Iowa, -.a.corp0ration of Iowa Original application September 18, 1952, -Serial No. 310,289. Divided and-this application March 4,1954, Serial No. 41'4;070

3 Claims. (Cl. 33382) This application is a division of.my application filed September 18, 1952, Serial No. 310,289, entitled Resonator Tuner.

This invention relates in general to high frequency tuners and in particular to cavity resonator tuners.

Cavity or coaxial resonators are used extensively at ultra high and very high frequencies as tuned circuits. It has been customary to construct cavity resonators with inner and outer conductors. They are shorted at one end and the lengths of the inner and outer conductors are such that the entire assembly will tune to a desired fre- 2 quency with a certain value of loading'capacity at the open end. Various methods have been used to make such elements continually tunable over a frequency range. One method is to use a shorting plunger between the inner and outer conductor that lengthens or shortens the effective iength of the cavity. Another method is by using a variable condenser across the open end of the coaxial resonator.

An object of the present invention is to provide an improvement in tunable cavity resonators wherein a very accurate response may be obtained.

Further objects, features and advantages of the invention will become apparent from the following description and claims when read in view of the drawings, in which:

Figure 1 illustrates one modification of a coaxial tunable resonator according to my invention,

Figure 2 is a modification of my invention, and

Figure 3 illustrates a third modification.

Figure 1 illustrates a cylindrical member which has a conducting disc 11 across one of the open ends. A shorting disc 12 is mounted to a plurality of downwardly extending wires 13. One of the wires 14 is connected to the plate 11 and the remaining ones passed through openings 15 formed in the plate 11 so that they are insulated from it.

An end loading capacitor C is connected between the upper end of the cylinder 10 and the disc 12. The cylinder 10 is grounded.

A lead 16 extends from the cylinder 10 to a multiple switch, designated generally as 17. The switch 17 has a plurality of movable members 18 that may be pivoted downwardly to engage the ends 19 of the rods 13. The members 18 are connected together electrically.

Various combinations of the switches 18 engaging the lower ends 19 of the wires 13 cause the resonant frequency of the cavity resonator to change. As more wires are shorted together by the switches 18, the characteristic impedance of the cavity is progressively reduced resulting in a higher resonant frequency. With the structure shown in Figure 1, the increments of frequency become smaller and smaller as more wires are shorted. The following table illustrates the results obtained with different values of C 2,717,363 Pgatented Sept. 6 1955 ice - 9 [ll-If.

The apparent action of the structure shown inFigure 1 .i tth twhenonly on wirelaactsas, th innercon c the characteristic impedance of the cavity is high but as each successive wire is shorted the characteristic impedance is decreased and the resonant frequency goes up. One wire is used as an inner conductor and the other wires appear as capacity across the circuit. This capacity is reduced as the wires are shorted together and at the same time the characteristic impedance is lowered.

A modification of the invention is shown in Figure 2 wherein a U-shaped conductor comprises a first leg 20 that has its lower end shorted to a disc 11. A transverse portion 21' is adjacent the opposite end of the member '20, and a downwardly extending portion 22 terminates above the disc 11.

A second conductor 23 extends downwardly from the member 21 and terminates above the disc 11. A shorting plunger 24 engages the members 20, 22 and 23. As the shorting plunger 24 moves from member 11 toward member 21, the conductors 20, 22 and 23 are first in parallel, but when the shorting plunger reaches the member 21 the conductors 22 and 23 form capacity applied across the condenser C and the only inductance in the circuit at this point is the conductor 20.

The plunger 24 extends through an opening 25 formed in the disc 11 and may be manually or automatically moved longitudinally of the cylinder 10. As the shorting bar travels from adjacent the disc 11 toward the member I 21, the frequency will be tuned from a high to a low frequency. The effect is to change the characteristic im-- pedance from low-to a higher impedance.

A third modification is illustrated in Figure 3 wherein the cylinder has been replaced by a rectangular shield member 26. A strip of conducting material 27 has one end 28 connected to an end 29 of the cover member and 0 extends upwardly and downwardly to form a leg 30 which terminates above the end 29.

The end loading capacitor C is connected from the end 39 to the cover member. A shorting plunger 32 shorts from the leg 27 to the leg 30 and may be moved longitudinally thereof.

A sheet of mica may be placed between the leg 30 and the wall 33 of the cover member to decrease the characteristic impedance when the shorting bar is adjacent the end 29. When the shorting plunger 32 is adjacent the end 29, the characteristic impedance of the cavity is low and the frequency high. When the shorting plunger is near condenser C member 30 and mica or other dielectric between the member 30 and the wall 33 appear to be capacitive across C The inductance of the center conductor is only the member 27 which is so spaced from the sides of the container so as to give a higher impedance. With such a structure, applicant has been able to tune from 280 to 360 megacycles.

It is seen that the invention described herein relates to an ultra high and very high frequency tuner wherein a continuous tuning characteristic may be obtained.

Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention as defined by the appended claims.

I claim:

1. A cavity resonator comprising, a cover member of conducting material, a closure member of conducting material attached to one end of said cover member, a first conducting member with one end attached to said closure member, a transverse conducting member with one end attached to the opposite end of said first conducting member, a second conducting member attached to the other end of said transverse conducting member and extending down toward said closure member but insulated from it, an end-loading capacitor connected between said transverse member and said cover member, and a shorting means extending between said first and second conducting members and movable relative thereto. 7

2. A cavity resonator comprising, a container member of conducting material, a conducting closure member connected across said container member, a first conductor with one end attached to said closure member, a transverse conducting portion connected to the other end of said first conducting member, a second conducting member with one end attached to the transverse conducting member and extending toward said closure member with its opposite end insulated from said closure member, and a shorting plunger movable longitudinally of said first and second conductors and engageable therewith.

3. A cavity resonator comprising, a container member of conducting material, a substantially U-shaped conducting member with one. leg longer than the other, the free end of said longer leg attached to said container member, the other leg insulated from said container member, a shorting plunger engageable with the first and second legs and movable longitudinally relative thereto to make an electrical connection therebetween, and an end-loading capacitor connected between the junction points of said legs and said container member.

No references cited. 

